How do I tile my textures when I am in Texture-Paint Mode?
You can use a brush texture (1) for which you assign your brush image (2) and use it in texture paint mode and with the "tiled" option (3). So you have your object texture painted with it (4).



To have a more regular result, you can also assign the brush image to your object (in its material (5)) and stretch its UV map (6):